Titrimetric Methods of Analysis

Rizk et al. [3] used 2,3-dichloro-5,6-dcyano-/)-benzoquinone as a redox titrant in the aqueous titration of penicillamine. Finely ground tablets were mixed with H20 and the mixture was filtered. The filtrate (or an injectable solution) was diluted with H20 and acidified with H3PO4 before titration with the redox titrant. The titration was conducted in anhydrous acetic acid using thiethylperazine dihydrochloride as the indicator. The endpoint was detected by a color change to green, and recoveries of penicillamine were 98.4-100.5%. 

Vollmer et al. [4] compared the Hg(II) acetate method described in the Code of Federal Regulations for the determination of penicillamine in bulk drug and formulations with (i) a nonaqueous lithium methoxide titration, (ii) a nonaqueous HCLO4 titration, and (iii) a colorimetric method with hydroxylamine. Method (ii) was unsatisfactory for bulk determinations. Method (i) was less precise than the Hg(II) acetate method, but gave satisfactory results for bulk drug and capsule samples. Method (iii) was the only method that gave satisfactory results in the presence of EDTA. 

Motonaka et al. [5] described a potentiometric method for the titration of ( -penicillamine with an iodide-selective electrode. An excess of methanolic 0.05 M iodine was added to a sample containing 8 pg to 6.2 mg of (/))-penicillamine. The solution was then diluted to 50 mL with H20, and titrated with 0.1 mM to 0.1 M AgN03. For 6 mg of (/))-penicillamine, the coefficient of variation was less than 0.3%. 

The reagent added to a solution containing the analyte and whose volume is the signal. 

The point in a titration where stoichiometrically equivalent amounts of analyte and titrant react. 

A colored compound whose change in color signals the end point of a titration. 

The determinate error in a titration due to the difference between the end point and the equivalence point. 

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In a titrimetric method of analysis the volume of titrant reacting stoichiometrically with the analyte provides quantitative information about the amount of analyte in a sample. The volume of titrant required to achieve this stoichiometric reaction is called the equivalence point. Experimentally we determine the titration s end point using a visual indicator that changes color near the equivalence point. Alternatively, we can locate the end point by recording a titration curve showing the titration reaction s progress as a function of the titrant s volume. In either case, the end point must closely match the equivalence point if a titration is to be accurate. Knowing the shape of a titration... 

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